Method of coating a fluorescent lamp tube



United States Patent 3,097,103 METHQD 0F COATING A FLUORESCENT L TUBEHorace H. Homer, Arlington, and Fred R. Taubner, Danvers, Mass,assignors to Sylvania Electric Products Inc.,

a corporation of Delaware No Drawing. Continuation of application Ser.No. 366,858, July 8, 1953. This application Aug. 12, 1959,

Ser. No. 833,136

2 Claims.

The present invention relates to fluorescent lamps :and the like, andparticularly to the fluorescent coating used in such lamps and tomethods of applying such coatings.

The coating applied to the lamp has a tendency to chip oil in spots.Various methods of improving the adherence have been tried, includingthe use of colloidal silica gel, but they have all reduced the phosphorefficiency.

We have discovered that a highly-purified powdered amorphous silica ofextremely small particle size, when used in a fiuosecent lamp phosphorcoating, will greatly improve the adhesion of the phosphor coating tothe glass, without decreasing the luminous efficiency.

The silica used is composed of discrete, amorphous particles which gointo suspension in water, as distinguished from silica that goes into ahydrated form in water, becoming silicic acid, or existing as a gel. The

silica should be highly purified to avoid absorption of the excitingultraviolet radiation used in the lamp. Amorphous silica can be obtainedwith a water content of less than 1%, and with the impurities of thecompletely dry silica being less than 1%. Such silica can be obtained inparticle sizes of about 0.02 micron.

The amount of superfine high-purity silica powder used should be greaterthan 0.05% by weight of the phosphor and less than 2.0%. Amounts of0.05% or less, do not improve the adherence, and amounts of 2.0% or morereduce the efliciency.

This is shown by the following tables, which give the results in lumensper watt (abbreviated L.P.W. in the tables) of tests on phosphorcoatings in the standard 40- watt fluorescent lamps, which are longglass tubes coated on the inside surface with phosphor, and havingoxidecoated electrodes at each end with a filling of mercury vapor andargon gas.

Test N0. 1 Lamps L.P.W. 100 hours Remarks Control 63.3 Chipped badly0.05 SiO 64.2 Chipped badly 0.5% SiO 64.0 Very little chipping Test N0.2 Lamps L.P.W. 100 hours Remarks Control 64.7 Chipped badly 0.1% SiO64.8 Less Chipping 0.5 S 64.2 Very little chipping 1.0% S10 64.6 No chpping 2.0% SiO 61.7 No chippmg The controls were standard 40 watt lampswith no silica added to the phosphor coating; the other lamps werestandard in all other respects but had superfine high-purity silicaadded to their phosphor coating in the amounts specified.

The coating suspension for the standard 40 watt lamp was made of thefollowing ingredients:

3,097,103 Patented July 9, 1963 300 grams phosphor powder, 4 cc. ArmeenCD, whichis a mixture of primary amines in the following proportions:octyl 8, decyl 9, dodecyl 47, tetradecyl 18, hexadecyl 8, octadecyl 5,octadecynyl 5.

255 cc. ethyl cellulose solution of approximately 12 seconds viscosity,containing the following ingredients in the following approximateproportions by weight: 200- second ethyl cellulose 2.9, dibutylp'hthalate 4.4, xylol 91.4, butanol 1.3.

The suspension for the other lamps was made of the above-listedingredients plus varying amounts of superfine high-purity silica powder.For the 0.05% lamps, 0.15 gm. of the silica was added to the abovesuspension, for 0.1%, 0.3-0 gm. was added, and for .5%, 1.0% and 2.0%respectively, 1.5 gms., 3.0 gms. and 6 grams were added.

In each case, the suspension was placed in a 1 quart ballmill with flintballs and rolled for 8 hours to insure proper dispersion of the powdersin the suspension.

The suspension was then applied to the open glass to be used in the lampin the usual manner, by being allowed to flow down the inside surface ofthe glass from the top thereof, as shown in U.S. Patent No. 2,412,954,granted December 24, 1946, to V. Zdancewicz. The tube was dried, thenbaked in a furnace in the usual manner, for about a minute at about 500C. The tube was in the furnace for several minutes, but only about aminute in the hottest or 500 zone. The tube was then finished into afluorescent lamp in the manner customary in the art.

The phosphor used in the particular tests cited was calciumhalophosphate, activated by-antimony and manganese, as described in theU.S. Patent 2,544,663 granted March 13, 1951, to D. F. Fortney and G. L.Moran. The addition of superfine high-purity silica is, however, usefulwith phosphors in general, for example manganese- :activated zincsilicate, manganese and lead activated calcium silicate.

This application is a continuation of our copending United States patentapplication Serial No. 366,858, filed July 8, 1953, and now abandoned.

What we claim is:

1. A method of coating a flourescent lamp tube, said method comprisingcoating the tube with a suspension containing between about 0.05% andabout 2.0% of superfine high-purity powdered silica by weight ofphosphor, said silica and phosphor being composed of separate particles,said silica having a particle size of about 0.02 microns and being ofthe type composed of discrete amorphous particles which go intosuspension in water, as distinguished from the type which goes into ahydrated form in water, and baking the coated tube.

2. A fluorescent coating on a transparent base, said coating comprisingpowdered phosphor particles and between about 0.05 and 2.0% of separatesuperfine high purity amorphous silica particles of an average particlesize of about 0.02 micron.

References Cited in the file of this patent UNITED STATES PATENTS2,278,742 Scott et a1 Apr. 7, 1942 2,621,134 Welch Dec. 9, 19522,838,707 Schwing et al June 10, 1958 2,841,505 Schmidt July 1, 1958FOREIGN PATENTS I 521,099 Great Britain May 13, 1940

1. A METHOD OF COATING A FLUORESCENT LAMP TUBE, SAID METHOD COMPRISINGCOATNG THE TUBE WITH A SUSPENSION CONTAINING BETWEEN ABOUT 0.05% ANDABOUT 2.0% OF SUPERFINE HIGH-PURITY POWDERED SILICA BY WEIGHT OFPHOSPHOR, SAID SILICA AND PHOSPHOR BEING COMPOSED OF SEPARATE PARTICLES,SAID SILICA HAVING A PARTICLE SIZE OF ABOUT 0.02 MICRONS AND BEING OFTHE TYPE COMPOSED OF DISCRETE AMORPHOUS PARTICLES WHICH GO INTOSUSPENSION IN WATER, AS DISTINGUISHED FROM THE TYPE WHICH GOES INTO AHYDRATED FORM IN WATER, AND BAKING THE COATED TUBE.